1. Field of the Invention
This invention relates generally to a superhigh frequency (SHF) receiver, and more particularly is directed to an SHF receiver which can receive satellite broadcast signals having different planes of polarization for adjacent channels.
2. Description of the Prior Art
In the case of satellite broadcasting, while the necessary band width of each channel is, for example, 27 MHz, the frequency spacing between adjacent channels is smaller than such band width, for example, is about 20 MHz, as shown on FIG. 1. Accordingly, in order to avoid radio interference between adjacent channels, it is known to make the planes of polarization of the satellite broadcast signals different for adjacent channels. By way of example, use has been made of a horizontal polarized wave and a vertical polarized wave, or a clockwise circular polarized wave and a counter-clockwise circular polarized wave, and so on.
In an SHF receiver according to the prior art which receives satellite broadcast signals having different planes of polarization for adjacent channels, when all the channels are sequentially selected, the channel selection is carried out in the sequential order of channel 1, channel 2, channel 3 . . . etc. In such case, for each channel change, the receiving plane of polarization of a polarizer is automatically changed-over so that the channel selection speed is necessarily slow. Alternatively, it has been proposed to provide an SHF receiver in which the receiving plane of polarization of the polarizer is fixed and alternate channels, for example, the odd-numbered channels, are selected sequentially. In this SHF receiver, when the other alternate channels, for example, the even-numbered channels, are selected, the user has to manually change-over the receiving plane of polarization of the polarizer and this is very bothersome for the user.